In various industries, objects may be formed from two or more different materials (such as two different alloys). For example, an object may be bimetallic and comprise a first metallic material and a second different metallic material that at least partially envelopes and covers the first metallic material. Hot pressing, or hot isostatic pressing, may be used to manufacture such an object by consolidating and diffusion bonding powder material together to form the object. Additionally, hot pressing, or hot isostatic pressing may be used to diffusion bond two or more objects together to form a single object.
Hot isostatic pressing of powder materials to manufacture an article involves initially forming a canister which defines the shape of the object to be manufactured. The canister is filled with powder material, evacuated to remove gases from the canister, and then sealed. The sealed canister is then hot isostatically pressed to consolidate the powder material within the canister and to diffusion bond the powder material together to form the article. During the hot isostatic pressing process the particles of the powder material are initially deformed to fill the inter-particle spaces, or voids, and then the particles of the powder material are diffusion bonded together. The canister is then removed from the article, typically by machining, by dissolving the canister in acid, or by a combination of machining and dissolving in acid.
One problem associated with the use of acids to dissolve and thereby remove the canister is that they may be precluded by environmental legislation. A further problem associated with acids is that the acids used to remove the canister may also cause damage to the article.
One problem associated with machining is that the use of machining to remove the canister may result in damage to the article and/or machining tool because the position of the interface between the canister and the article and the positions of features of the article are not known after the hot pressing process, or hot isostatic pressing process. The position of the interface between the canister and the article after consolidation of the powder material is not known accurately because of process variations in the shrinkage of the particles of the powder material and the collapse of the canister as the inter-particle spaces, or voids, are filled by the deformation of the particles of the powder material.